1. Field of the Invention
This invention relates to contact lens care compositions and methods. More particularly, this invention relates to solutions for treating and disinfecting soft contact lenses, particularly high water content ionic hydrophilic lenses.
2. Description of Related Art
Hydrophilic soft contact lenses, which are also referred to as hydrated gel lenses, are prepared by copolymerizing hydrophilic organic monomers having an olefinic double bond with a small amount of a cross-linking agent, usually having two polymerizable, olefinic double bonds. These lenses are usually based upon poly(hydroxyalkyl)methacrylates such as poly(hydroxyethyl)methacrylate, cross-linked with, for example, ethylene glycol dimethacrylate, a hydroxyethyl dimethacrylate. The hydroxyl groups of the hydrated gel lenses render the lenses hydrophilic, i.e. they wet easily and absorb water. Other functional groups, such as carboxylic acid moieties from methacrylic acid copolymers, also contribute to lens hydrophilic character. With water absorption, the lenses also may take up chemicals dissolved in the water.
Hydrophilic contact lenses can be divided into four groups, namely, low and high water content nonionic lenses (Group I and Group II) and low and high water content ionic lenses (Group III and Group IV). The care of these types of hydrophilic lenses presents specific problems. However, the care of high water content ionic lenses (Group IV) can be particularly difficult due to the fact that many of the components of cleaning and disinfecting products have a tendency to bind to these lenses more than to other types of lenses.
Group IV lenses contain a relatively large number of exposed carboxylic acid groups, each of which is largely ionized, bearing a negative charge at physiologic pH. When contact lens care products containing compounds bearing positive charges are used with Group IV lenses, an ionic interaction can take place between the lenses and those components. Use of products containing such components can produce undesirable clinical symptoms in some persons, such as diffuse corneal staining and product intolerance.
Subsequent to the introduction of hydrophilic lenses, it was found that, those lenses, due to their gel structure and/or their affinity to adsorb or absorb materials, had a tendency to complex and concentrate most of the preservatives and disinfecting agents known at that time. The most common preservatives and disinfecting agents known at that time were sorbic acid, thimerosal, benzalkonium chloride and chlorhexidine. It was found that many of these preservatives and disinfecting agents become concentrated in the lenses to a sufficient degree that when the lens is placed in the aqueous environment of the eye, the preservatives or disinfectants are released from the lens and cause eye irritation. This problem was found to be particularly severe with positively charged preservatives or disinfecting components.
Isotonic aqueous solutions containing the polymeric quaternary ammonium chloride compound, Polyquad.RTM. (registered trademark of Alcon Laboratories, Inc.) which is also known as Onamer.RTM.M (registered trademark of Millmaster Onyx Group) has been used successfully to provide disinfecting and preservation properties to contact lens treating solutions, eye drop solutions and preserved saline solutions. The chemical name for Polyquad.RTM. is.alpha.-4-[1-tris(2-hydroxyethyl)ammonium-2-butenyl]poly[1-dimethylammon ium-2-butenyl]-.omega.-tris(2 hydroxyethyl)ammonium chloride. The salt has an average molecular weight generally in the range of from about 2,000 to about 30,000 and preferably in the range of about 3,000 to about 14,000. The compound has the general formula: ##STR1## wherein X is a pharmaceutically acceptable anion, and in the case of Polyquad.RTM. is chloride. The effective compound is a cation which is derived from the disassociation of a salt that has a pharmaceutically acceptable anion such as acetate, sorbate, or a halogen, preferably chloride or bromide.
Ophthalmic compositions containing Polyquad.RTM. and methods for disinfecting contact lenses with solutions containing this polymer are disclosed in commonly assigned U.S. Pat. Nos. 4,525,346 and 4,407,791 both issued to Stark, June 25, 1985 and Oct. 4, 1983, respectively. These patents describe various types of ophthalmic products containing Polyquad.RTM., including products for treating contact lenses (e.g., disinfecting solutions) and products for more general ophthalmic use (e.g., comfort drops).
The compositions of the present invention comprise a polymeric quaternary ammonium compound, such as Polyquad.RTM., disclosed in the Stark patents referred to above. However, the compositions and methods described herein represent an improvement over those disclosed in the Stark patents because the present compositions and methods can be used to treat Group IV contact lenses. The compositions and methods disclosed in the Stark patents can also be used to treat Group IV lenses. However, it has been found that without the improvements described herein the compositions and methods of Stark may result in binding of Polyquad.RTM. to the contact lens, at least with respect to some types of lenses and some types of lens care regimens. This binding problem has stood in the way of commercial use of the Stark compositions and methods in conjunction with Group IV lenses. The problem has been solved by the present invention.